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One of my regular readers wrote to me today, about an advert that she’d stumbled across recently. I asked if I could reproduce it here (changing some names) as it’s a very good example of someone thinking critically about claims made for a particular product.

‘Jane’ writes:

OK, my skeptic-o-meter is going off big time… have you ever heard of Product X?  It’s a ‘natural’ insect repellent which makes some interesting claims…
 
Product X works in 3 very unique ways:
1.Product X hides the user from the mosquito making it difficult for the insect to find you.
[Me: given that mosquitoes use exhaled CO2 as one way to find their next bite, using body heat as an extra guide, this sounds rather unlikely. It may possibly mask your odour, which is another cue that female mosquitoes use when looking for a blood meal.]
 
2.If the mosquito does actually land and tries to bite, Product X will interfere with the insect’s nervous system making it difficult for them to bite at all.
[Me: that is possible. I've seen claims that the essential plant oils contained in products like this interfere with insect nervous systems by disrupting the action of a neurotransmitter called octopamine. There is certainly evidence from both in vitro in vivo studies that essential oils have an effect on insect nervous systems eg here & here, with suggestions that these oils could be used as both pest repellents & pesticides. But perhaps it's just that ,when they get up close & personal, the mozzies are put off by the smell.
Just as an aside, octopamine's also found in vertebrates but there's been little research into how it operates.This hasn't stopped people promoting its use as a slimming aid... ]
 
3.Elements of Product X also have skin soothing properties to ease the discomfort of previous bites.
Product X is also biodegradable and the packaging is recycled and recyclable, so its good news for the environment too. 
Buy this 2 pack now and enjoy your summer free from bites and itches.
·    gentle formula
·    water resistant
·    6 hours protection
·    contains no DEET or Citronella
·    great for camping, school trips
Pack contains: 2 x 100ml Product X natural repellent

"As a regular worldwide traveller I can recommend Product X in all climates and conditions. It's one of the first things into the suitcase ! Try it yourself and you will be converted." Author Brian Jeffrey 
I like the endorsement from an author, particularly one who has no listings on Amazon…
 
It appears to tell us what’s not in the product, but not what is in it… the website also claims ’Contains NO chemicals yet proven to be as effective as chemical based products such as DEET’ but doesn’t appear to substantiate this claim. 
 
[Me: 'contains no chemicals is a common claim but since everything is made up of 'chemicals' it's an inaccurate one. If the product somehow did manage to contain no chemicals at all then it would also be effect-free. Unless it operates on homeopathic principles... - let's not go there! But from what I can find, it contains volatile plant oils, which are definitely chemicals. 'Natural', perhaps, but definitely not 'chemical-free.] 
 
Lots of online stores selling this product have personal testimonials, mention that in ’trials’ it has outperformed traditional repellants, and one even claims it has been road-tested by military personnel… but all with a  surprising (!) lack of actual evidence, or links to aforementioned trials.
 
Is my skeptic-o-meter functioning correctly??
 [Me: oh yes, very definitely! Having lots of testimonials, but no actual data, should always make you question the claims made for a product.]
 
Regards,
Jane